With the alteration of refrigerant gas or refrigerators to hydrogenated fluorocarbon (HFC) such as R-134a (CH.sub.2 F--CF.sub.3) which is nondestructive to the ozone layer, mineral oils or alkylbenzene compounds having been heretofore used as lubricating oils for refrigerators have come not to be used therefor because they have no compatibility with the refrigerant gas. Instead of those oils or compounds, other compounds such as polypropylene glycol, polypropylene glycol monoalkyl ether and polypropylene glycol dialkyl ether have come to be used as lubricating oils for refrigerators. However, uhese compounds are low in compatibility with R-134a, and among these compounds, high-viscosity compounds showing a kinematic viscosity at 100.degree. C. of not less than 15 cSt have such a problem that they exhibit poor performance as lubricating oils for refrigerators such as those for automotive rotary air-conditioner because of low compatibility with R-134a.
This problem is involved not only in the hydrogenated fluorocarbon which is nondestructive to the ozone layer but also in hydrogenated chlorofluorocarbon (HCFC) which is small in ozone depletion potential and mixtures of the hydrogenated fluorocarbon and the hydrogenated chlorofluorocarbon.
Examples of the hydrogenated fluorocarbons include the above-mentioned R-134a and R-152a, and examples of the hydrogenated chlorofluorocarbons include R-22, R-123 and R-124.
By the way, it is known that if a lubricating oil having polarity such as an ester group is used to enhance the compatibility with R-134a, the lubricating oil is deteriorated in lubricating performance on surface of a metal device.
Accordingly, there has been heretofore desired no only the advent of compounds having high viscosity and showing high compatibility with R-134a but also the avent of lubricating oils for refrigerators containing these compounds.